A switch-based sensor apparatus is disposed between the bottom cushion and frame of a seat. The sensor apparatus includes upper and lower rigid and generally parallel force translation plates biased apart by a set of springs, and a switch assembly. The force translation plates are joined so as to pre-load the springs while permitting closing movement between the upper and lower force translation plates in response to occupant seat force that exceeds the pre-load force of the springs. The switch assembly includes a circuit board and elastomeric switch pad defining one or more switch elements that are actuated by a prescribed closing movement between the upper and lower force translation plates for electrically detecting the presence of a seat occupant.